Connection Pool Sizing - Sun Microsystems Sun GlassFish Enterprise Server 2.1 Tuning Manual

Initial and Mimimum Pool Size
"Timeout Settings" on page 78
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"Isolation Level Settings" on page 79
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"Connection Validation Settings" on page 79
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Pool Size Settings
The following settings control the size of the connection pool:
Initial and Size of the pool when created, and its minimum allowable size.
Mimimum Pool
Size
Maximum Pool Upper limit of size of the pool.
Size
Pool Resize Number of connections to be removed when the idle timeout expires. Connections that have idled for
Quantity longer than the timeout are candidates for removal. When the pool size reaches the initial and minimum
pool size, removal of connections stops.
The following table summarizes pros and cons to consider when sizing connection pools.

Connection Pool Sizing

TABLE 3–4
Connection pool
Small Connection pool
Large Connection pool
Timeout Settings
There are two timeout settings:
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78 Sun GlassFish Enterprise Server 2.1 Performance Tuning Guide • January 2009
Pros
Faster access on the connection table.
More connections to fulfill requests.
Requests will spend less (or no) time in the
queue
Max Wait Time: Amount of time the caller (the code requesting a connection) will wait
before getting a connection timeout. The default is 60 seconds. A value of zero forces caller
to wait indefinitely.
To improve performance set Max Wait Time to zero (0). This essentially blocks the caller
thread until a connection becomes available. Also, this allows the server to alleviate the task
of tracking the elapsed wait time for each request and increases performance.
Cons
May not have enough connections to
satisfy requests.
Requests may spend more time in the
queue.
Slower access on the connection table.